This is easily my favorite skull in my collection. Not is it only from an extinct dog-like predator, but it has fossilized brain material preserved which is very rare. It's a small skull but in extremely good condition.
Late Eocene - Early Oligocene, Brule Formation, South Dakota, 35 Million years old. An extremely rare and well-preserved fossil of the Hesperocyon Gregarius, an early dog that roamed the plains of North America. Brain and teeth are extremely well preserved. 3-3/4" x 2" x 2-1/4"
Image of what Hesperocyon may look like:[link]